PowerPoint 2013: Images in presentation disappear - and are replaced with 'The image part with relationship ID rId2 was not found in the file'

I've used PPT for 20 years and started using PowerPoint 2013 through Office 365 2 months ago and this has happened to me 4 times.

1. I create a presentation (Using copy and paste and/or insert to include pictures and other images)

2. After working on the presentation for a while I save the file and realize all the images (except smart art) are gone and replaced with the message above.

3. I have reinstalled PPT 2013 and it happened again. I have documents that are 50 pages long and have had to insert new images (Hours of lost work) then 3 days later it happens again.

Not sure if it is related but I've noticed that once in a while when I try to save a document (Happens in Word and Outlook Calendar items) it tells me the file is locked and makes me save under a new name.